1. (a.) Impossible to be omitted, absolutely necessary\ or requisite.

2. (a.) Not admitting dispensation; not subject to release or exemption.

3. (a.) Unavoidable; inevitable.

bare necessities basic bedrock call for called for cardinal central compelling compulsory crucial demand demand for demanded desideration desideratum essential essentials focal fundamental imperative important in demand indicated ineluctable inescapable irreducible irreductible irreplaceable key life-and-death life-or-death mandatory material must must item necessaries necessary necessities necessitous necessity need need for needed needful obligatory occasion of the essence of vital importance prerequirement prerequisite required requirement requisite requisition sine qua non substantive the necessary the needful unavoidable unforgoable urgent vital want wanted